Gaz,
To follow my theme - it depends! What you want to make, wet / dry timber, cross or end grain. Most will tackle all, but some excel in one type, others in other types of work. If you only ever want to hollow miniature forms, that will rule some options out and the reverse is true.
I would echo Delboy's advice but to answer your question directly (with beginner in mind - pls correct me if that is not the case)
Low budget - google oland tool. Homemade with bit of steel rod and hss tip from any tool merchant. limit projection of tip to limit torque placed on tool. Pros, cheap and best suited to end grain work although can do others. Cons, scraping tool so finish can be rough until get hang of it, can be bit aggressive / 'catchy'.
High budget- munro hollowing tool (5/8" shaft). great tool, easy to use. Pros - Excels in wet end grain but v.good all rounder. quick to learn. Cons - cost. err - that's about the only one!
This is a wide market, basically all either cutting or scraping tools though. cutting tools sub-divided into shielded and open. Ask if you have any other specific Qs but as above, i'd really suggest cutting you teeth on the outside shape before trying to do the inside blind!
BRgds
Simon